Formation plugging method



g- 10, 1965 D. R. HOLBERT 3,199,588

FORMATION PLUGGING METHOD Filed Oct. 31, 1961 INPUT A PRODUCTION r MATERIAL MATERIAL D POLYMERIZD INVENTOR. DON R. HOLBERT ATTORNEYS United States Patent 3,i99,588 FGRMATEQN PLU'GGENG METHGD Don R. Holbert, Tulsa, @lsla, assignor to fiiriclair Research, Ind, Wilmington, Del, a corporation of Delaware Filed Get. 31, 1961, Ser. No. 14?,639

9 Claims. (Cl. res-as This invention relates to a process for plugging subterranean fissures communicating with a well, particularly fissures communicating from an input to an output well.

Various methods have been devised for the recovery of oil and gas from subterranean formations, which, at this time, may be termed conventional. These methods are to a great extent, supplementary to each other and can be presented in the order in which they are applied to a given formation. In the first instance, upon the establishment of communication from the surface of the earth to a subterranean oil and gas bearing formation, the oil and gas are frequently forced to the surface under the pressure prevailing in the formation. Following the exhaustion of a significant amount of pressure in the formation such that the natural flow of oil up the Well bore ceases, recovery of the oil may be continued by pumping means. However, when a negligible amount of oil ilows freely to the well for pumping, the formation is sometimes repressured to drive the oil from the formation to the well. The oil can be forced into the well from an adjacent formation by driving a fluid, e.g. water or other liquid or gaseous medium, through the formation as from an input to an output Well. The processes employing a driving fluid through the formation to recover oil after pumping alone becomes disadvantageous, are sometimes referred to as secondary recovery methods.

A formation fissure is an area of relatively high fluid acceptance which can be natural or induced as a result of measures taken to enhance the productivity of the producing wells. The presence of fissures of high permeability between the input and output Wells, however, seriously aifects the efficiency of the drive since the driving medium will tend to traverse the subterranean area through the fissures instead of the oil bearing formation. For instance, the fissures or areas of high fluid permeability relative to other partsof the stratum, are generally in an underground formation characterized by a substantial vertical permeability. Thus, although measures have been taken to seal the portion of a fissure adjacent a well bore, such limited plugging has generally been ineffective as the driving fluid employed in secondary recovery operations, for instance, merely lay-passes the plug by virtue of traveling through the area of vertical permeability to the unplugged portion of the fissure. To overcome this problem, a large portion of the length of the fissure between the input and output Wells should be plugged.

An object of the present invention is the provision of a process for plugging a substantial length of a subterranean fissure communicating from an input to an output Well. Another object is the provision of such a process for expeditiously plugging such a fissure permitting use of only one of the wells for injection of the plugging composition. Anot er object is the provision of a process of this type which can be conducted from the input or production well.

In the process of the present invention, resin-forming material containing polymerizable organic monomers which can be catalyzed (triggered) to polymerize, set and form into a solid or semi-solid gel-like plug, are precatalyzed to set at a time sufficient to permit passage of the material into the input well and through the fissure to a position adjacent, e.g. at least about 60 or 75% of the distance to, the output well before becoming essen-- tially immobile, preferably before reaching a viscosity ex Patented Aug. 10, 1965 ceeding about 15 centipoises. The catalyzed resin is conducted into the input well and through the fissure to the position adjacent the output well to set and plug the fis sure in this position, the initial portions setting and restricting or blocking the flow of resin-forming material to the production well. Upon further pumping of the material into the fissure, the block in the fissure, in exerting back pressure, permits the material to be injected at greater injection pressures to force material into areas adjacent to the fissure and efficiently seal the fissure. The injection of resin-forming material is stopped soon enough to enable removing, e.g. flushing, any residual portions in the input well before it sets and deleteriously affects secondary recovery operations. It is preferable to have both ends of the fissure free to maintain accessibility between the input and output wells and the formation. Thus it may be desirable to avoid plugging the fissure for a distance extending from the input and output wells into the fissure generally of about 5 to 50 feet or even up to 100 feet or more dependin upon the distance between the wells. This results in plugging only the mid-portion of the fissure and usually at least about 66 or of the fissure length. When the fissure is sealed, at driving medium used in secondary operations is employed more efiiciently as its dissipation in the fissure is severely limited or eliminated.

The amount of resin-forming material required to plug the fissure and the trigger time interval, a predetermined time after. which the catalyzed resin-forming material will set; can be estimated by the results of a pre-run chemical or radioactive tracer test, for instance, by measuring the volume of material injected after the addition of a tracer chemical into it and noting the time it takes the tracer to arrive in a producing well. Suitable adjustments to this time should also be made by adding the time required to incorporate the catalyst into the material. The time is also reduced, for instance by about 1 to 30 percent, to preclude the introduction of catalyzed resinforming material into a production well, for instance, when the operation is being conducted from the input well.

The resin-forming material is conducted into the fissure at pressures below fracturing pressures and is advantageously conducted into the fissure in increments which can be in amounts from about 5 or 10 to 25 percent of the total amount of material destined to plug the fissure. Each increment is conveniently catalyzed to polymerize in the same given time interval but progressively shorter times may be employed since travel time to the position of plugging may decrease with each injection at a given pumping rate.

The first increments pumped or injected will polymerize first to form .a plug at the leading edge of the material moving through the fissure. As pumping is continued, to regressively plug the fissure, the injection pressure will rise causing a squeezing of the material in and around the fissure or channeling system. Material can be pumped into the fracture until the permeability of the fissure is reduced as indicated by an increase in the injection pressure or a decrease in the pumping rate at a given injection pressure or a combination of these. It is desirable to obtain an increase in pressure drop or frictional resistance to fluid flow across the formation to increase oil displacement. Pumping can be stopped when pressure has been built up to the desired level and the input well tubing and bore have been displaced free of the material. The well can then be shut in to allow complete polymerization of the resin-forming material to substantially plug the fissure.

The process of this invention can be illustrated by reference to the drawing which shows input and production wells 1 and 2, respectively penetrating an oile73 bearing formation 3 having high permeability thief fissure 4 which extends between the two wells. Although the process is illustrated by having it conducted from the input well, it will be obvious to those versed in this art that it can also be conducted from the production well. The fissure is to be plugged from position A to position B. It is sealed off with packers according to procedures well known in the art to provide for the selective injection of resin-forming material into the fissure. It is estimated that it will require about 1500 gallons of resin-forming material to plug the fissure. The time at a given pumping rate it will take an initial portion of the resin material upon injection into the well to arrive at position B is estimated at 60 minutes.

In accordance with the process of this invention, 1500 gallons (about 85% of the indicated fracture volume as determined by the tracer test at injection pressure) of AM-9 resin-forming material (an aqueous solution consisting essentially of about 10 percent of a mixture of N,N'-methylene-bisacrylamide and 95% acrylamide) precatalyzed to set in 60 minutes after injection with 2% ammonium persulfate and .4% of nitrilotrispropionamide is injected into the input well at a pressure of up to about 1000 p.s.i. in 150 gallon increments. The increments, each processed to set in 60 minutes, at reservoir temperature of about 100 F., are injected in succession. The first increment arrives at position B in the fissure in about 60 minutes, sets and plugs the fissure, exerts a flow restriction on the second increment, squeezing portions of it into areas C and D adjacent the fissure. The second increment has a like efiect on the third and so on to regressively plug the fissure. During the operation the injection pressure went from O to about 1000 p.s.i. at a rate of 500 barrels per day.

The resin-forming material employed in this process should be capable of hardening or setting at temperatures in the fissures which in many cases are between 50 and 200 F. They include those which form modified alkyd or polyester-type resins, styrene-divinylbenzene copolymers, and those described below although these are not to be considered limiting.

The liquid resin-forming materials polymerized in the above example of the process of the present invention are particularly suitable for use in the well bore treating field and include an aqueous solution of an alkylidene bisacrylamide and ethylenic comonomer, the bisacrylamide having the formula:

is a hydrocarbon residue of an aldehyde containing, for instance, from about 1 to and preferably from about 1 to 5 carbon atoms, e.g. formalde-, aceta1de-, and valeraldehyde; but usually about 1 to 3 carbon atoms; and R is a member of the group consisting of hydrogen and a methyl radical. v

The other comonomer is a solid, liquid or gaseous ethylenic (i.e. contains at least the (3=C radical) compound with a solubility of at least about 2 percent by weight, and preferably at least about 5 percent, in Water and which copolymerizes with the aforesaid bisacrylamide in an aqueous system. Although not essential in practicing the invention, it is preferred to select an ethylenic comonomer which is preferably soluble or at least selfdispersible in water with appropriate stirring, as such, for example, methylene-bisacrylamide, which is capable of polymerizing.

In addition to the comonomer N .Nmethylenebis-acrylamide set out in the examples hereinafter, any of the alkylidene bisacrylamides corresponding to the above formula which are described and claimed in Lundberg Patent No. 2,475,846 hereby incorporated by reference, or mixtures thereof may be used as cross-linking agents. Only slight solubility is required of the alkylidene bisacrylamide in view of the small amount used; therefore, this component may have a water solubility as low as about 0.02 percent by weight at 20 C. but a solubility of at least about 0.10 percent is more desirable for general purposes.

A wide variety of ethylenic comonomers or mixtures thereof are copolymerizable with the alkylidene bisacrylamides; those having a formula containing at least one C C grou preferably containing from about 1 to 8 carbon atoms, hereinafter referred to as the ethenoid group, and having appreciable solubility in water are suitable for use in the present invention. See US. Patent No. 2,801,985, hereby incorporated by reference. As set forth in this patent, the unsubstituted bonds in the ethenoid group may be attached to one or more of many different atoms or radicals including hydrogen, halogens, such as chlorine and bromine, cyano, aryl, aralkyl, alkyl, and alklyene with or without solu biliziug groups attached to these hydrocarbons. In addition, the substituents on the ethenoid group may comprise one or more hydrophilic groups including formyl, methylol, polyoxyalkylene residues and quaternary ammonium salts radicals,

where each R is hydrogen, alkylol, lower alkyl or a polyoxyalkylene radical; and COOR' and CH COOR', where R is a H, NH alkali metal, alkaline earth metal, organic nitrogenous base, alkylol, lower alkyl or polyoxyalkylene radical. The large number of combinations and proportions of the various suitable substitutents makes it impractical to list all compounds in this category which may be employed. The water solubility of these substances is known to depend chiefly on the number and type of hydrophilic and hydrophobic radicals therein; for example, the solubility of compounds containing an alkyl radical diminishes as the length of the alkyl chain increases and aryl groups tend to decrease water solubility whereas the aforesaid hydrophilic substituents all tend to improve the solubility of a given compound in water. Accordingly, the comonomer should be selected according to chemical practice from those containing sufiicient hydrophilic radicals to balance any hydrophobic groups present in order to obtain the requisite Water solubility of monomer.

Among the water-soluble ethenoid monomers, those containing an acrylyl or methacrylyl group are especially recommended. These are exemplified by N-methylol acrylamide, calcium acrylate, methacrylarnide and acrylamide. Other suitable ethenoid compounds are acrylic acid; other N-substituted acrylamides, such as N-methylacrylamide, N 3 hydroxypropylacrylamide, dimethylarnino-propylacrylamide, N-ethylol acrylamide; acrylonitrile; saturated alkyl esters of acrylic acid, i.e. methyl acrylate, B-hydroxyethyl acrylate; ethylene glycol and polyethylene glycol acrylates, an example being the reaction product of ,B-hydroxyethyl-acrylate or acrylic acid with about 1 to about 50 mols or more of ethylene oxide; salts of acrylic acid, i.e. magnesium acrylate, sodium acrylate, ammonium acrylate, zinc acrylate, ,B-amim-ethylacrylate, fl-methylaniinoethyhacrylate, guanidine acrylate and other organic nitrogenous base salts, such as diethylamine acrylate and ethanolamine acrylate; quaternary salts like alkyl acrylamidopropyl dimethylamino chloride; acrolein, fl-car- 53 boxyacrolein, butenoic acid; a-c-hloroacrylic acid }chloroacrylic acid; as Well as methacrylic acid and its corresponding derivatives.

Maleic acid and its correspondingderivatives including partial esters, partial salts, and ester salts thereof; maleamic, chloromaleic, fumaric, itaconic, citraconic, vinyl sulfonic, and vinyl phosphonic acids and their corresponding derivatives and mixtures thereof. Derivatives of this kind and other suitable compounds include afi-(liChlOIO- acrylonitrile, methacrolein, potassium methacrylate, magnesium methacrylate, hydroxyethyl methacrylate, zinc B-chloroacrylate, trimethylamine methaclylate, calcium a-chloromethacrylate, diethyl methylene succinate, methylene succindiamide, monomethyl maleate, maleic diamide, methylene maloanamide, diethyl methylene malonate, methyl isopropenyl ketone, ethyl Vinyl ketone, propyl vinyl ketone, vinyl formate, vinyl lactate, vinyl acetate, vinyl bromoacetate, vinyl chloroacetate, vinyl pyrrolidone, allyl levulinate, allyl alcohol, methallyl alcohol,

iallyl carbonate, allyl lactate, allyl gluconate, di(flaminoethyl) maleate, di(methylaminoethyl) maleate, di- (N,N'-dirnethyl-B-aminoethyl) maleate, sulfonated styrene, vinyl pyridine, maleic anhydride, sodium maleate, ammonium maleate, calcium maleate, monopotassium maleate, monoammonium maleate, monomagnesium maleate, methyl vinyl ether, N-aminoethyl maleamide, N-aminoethyl maleimide, alkyl aminoalkyl maleamides, N-vinyl amines, N-allyl amines, heterocyclic ethenoid compounds containing nitrogen in a tertiary amino group, and the amine and ammonium are salts of said cyclic compounds, N-vinyl acetamide, N-vinyl-N-methyl formamide, N-vinyl-N-methylacetamide, N-vinyl succinimide, N-vinyldiformamide, N-vinyl diacetamide, vinyl sulfonyl chloride, vinyl sulfonic acid salts, vinyl sulfonic acid amides, vinyl oxazolidone, allyl amine, diallylamine, vinyl methyl pyridinium chloride, and allyl trimethyl ammonium chloride to name only a few of the operative compounds.

he preferred resin-forming composition employed in the process of the present invention is in an aqueous medium and has an initial viscosity approximating that of water. These compositions can he formed by dissolving a mixture of acrylamide and N,N-methylenebisacrylamide in fresh water. Generally, this mixture contains about 1 to 25 weight percent of N,N'-n1ethylenebisacrylamide and about 99 to 75 weight percent of acrylamide. The aqueous solution will usually include from about 5 weight percent of this mixture to its limit of solubility and preferably this amount is about 5 to 25 percent.

Although the acrylamide as such is preferred, its nitrogen atom could be substituted as with a hydroxy methyl or a hydroxy ethyl group.

A redox catalyst system can be used to catalyze the resin-forming material and such a system generally includes an oxidizing agent and a reducing agent. The oxidizing agent which can be advantageously incorporated into the resinous mixture according to the present invention is employed in catalytic amounts and these amounts will generally be from about 0.01 to 2.0 weight percent and preferably from about 0.1 to 0.6 weight percent based upon the weight of the polymerizaole monomers. The oxidizing agents include, for instance, any of the usual water-soluble peroxy catalysts derived from per-acids such as persulfuric, perchloric, perboric and permanganic and their salts. For example, ammonium potassium and sodium persulfates, hydrogen peroxide, the alkali metal and ammonium perchlorates and the like may be employed.

The reducing agent can be employed in catalytic reducing amounts to aid in effecting copolymerization of the copolymerizable monomers containing the catalyst or oxidizing agent. It is generally employed in amounts equivalent to generally from about 0.01 to 10 percent, usually about 0.1 to 7 percent and preferably about 0.1 to 3 weight percent based upon the weight of the polymerizable monomers. Among the reducing agents that can 6 be employed are the oxygen-containing sulfur compounds such as the alkali metal, e.g. sodium or potassium bisulfites, and nitrilo-tris-propionamide. Examples of typical oxidizing agent-reducing agent combinations are sodium persulfate, potassium persulfate, or ammonium persulfate and nitrilo-tris-propionamide.

The amounts of each of the oxidizing agent and reducing agent can be varied to give the desired copolymerization time which may range from about 10 to 120 minutes, for instance, depending upon the location of the fissure. For instance, a weight ratio of oxidizing agent to reducing agent in the resin-forming material after incorporation of the reducing agent by the method of the present invention of 1 to 2 in an aqueous solution containing 20 weight percent of the acrylamide and N-N'- methylenebisacrylamide percent acrylamide and 5 percent N-N-methylenebisacrylamide) will give a polymerization time at 70 F. of about 60 to minutes when the oxidizing agent plus reducing agent is about 0.5 to 1.5 percent of aqueous solution of the resinous material.

In addition to the above-mentioned ingredients, the resin-forming mixture employed in the process of the present invention may include other components. For instance, an inorganic metal salt can be employed in polymerization expediting amounts if it is desired to shorten the set time of a catalyzed material and can be incorporated into the resin-forming mixture.

The inorganic metal salts which can be employed in the present invention are the halides of metals of Groups I to III of the periodic table of elements. The halides of halogens having an atomic number from 17 to 35 are preferred. The halides include the alkali and alkaline earth metal halides such as sodium chloride, potassium chloride, magnesium chloride, strontium chloride and calcium chloride as Well as their corresponding bromides. Other halides include zinc chloride and aluminum chloride. The halides as specified are not necessarily equivalent from the standpoint of enhancing the polymerization of monomers. Among the halides, calcium chloride and zinc chloride are outstanding in performance, and sodium chloride performs exceptionally well.

The polymerization expediting amounts are those amounts which will enhance the polymerization rate of the monomers included in the resin-forming mixture and will generally range from about 5 to 35 or more weight percent based upon the aqueous resin-forming mixture and salt. Calcium chloride can also be used in various amounts such as about 5 weight percent of the aqueous resin-forming mixture and calcium chloride, or in amounts up to its solubility, to provide advantageous electrical conductivity characteristics, preferably a conductivity between that of fresh H 0 and brine when used in well treating operations, to enable detection of the presence or absence of resin-forming material in the Well bore. Calcium chloride can also be present in amounts ranging from about 15 to 35 or more weight percent based on the aqueous resin-forming mixture and calcium chloride, for instance up to the limit of solubility, to provide advantageous weighted or specific gravity characteristics such that the resin-forming material can be efficiently displaced into the permeable area before it can be dispersed by physical contact with salt or fresh water present in the Well bore, i.e. the resin-forming material is made heavier than the salt or fresh water and is resistant to dispersion.

It may be desirable to exercise care as to the amount of additives incorporated into the resin-forming material and this will depend upon the specific additive employed. In general, the initial viscosity of the material at the temperatures and pressures encountered in the bore hole is such that it has a viscosity of up to about 10 centipoises, advantageously about 1 to 5 centipoises at these conditions.

It is claimed:

'1. A process for selectively plugging an oil-bearing, subterranean, high-permeability area which extends between and communicates with first and second well bores spaced apart from each other, which comprises introducing catalyzed resin-forming material into said first bore and through the high-permeability area to a position at least about 60 percent of the distance to said second bore at which position the catalyzed resin-forming material sets to plug said high-permeability area, and pumping at an increased pressure from said first bore an amount of catalyzed resin-forming material into the high-permeability area, said latter catalyzed resin-forming material being pumped against the resistance of previously set catalyzed resin-forming material, to regressively plug the high-permeability area from said position to a position in said area in the vicinity of said first bore, thereby plugging at least about 60 percent of the length of the high-permeability area.

2. The process of claim 1 wherein catalyzed resin-forming material is conducted into said high-permeability area in increments of about 5 to 25% of the total resin-forming material injected into said area.

3. The process of claim 2 wherein the catalyzed resinforming material is an aqueous solution consisting essentially of water and a mixture of (-a) about 1 to 25 Weight percent of a monomeric alkylidene bisacrylanlide of the formula is a hydrocarbon residue of an aldehyde containing from about 1 to 10 carbon atoms and R is of the group consisting of hydrogen and methyl, and (b) about to 99 weight percent of another ethylenic monomer copolymerizable with (a).

4. The process of claim 3 wherein the resin plug is at least about 5 feet from each of said first and second bores.

5. The process of claim 3 wherein the resin-forming material is precatalyzed with a Redox catalyst system including an oxidizing agent and a reducing agent.

6. The process of claim 5 wherein the bisacrylamide is N,N-methylenebisacrylamide.

7. The process of claim 6 wherein the ethylenic monomer is acrylamide and the oxidizing agent is ammonium persulfate.

8. The process of claim 7 wherein the reducing agent is nitrilotrispropionamide.

9. The process of claim 1 wherein the resin plug is at least about 5 feet from each of said first and second bores.

References Cited by the Examiner UNITED STATES PATENTS 2,781,850 2/57 Nowak 16633 2,786,530 3/57 Maly 166-10 2,801,984 8/57 Morgan et al. 166-33 2,940,729 6/60 Rakowitz 166-33 CHARLES E. OCONNELL, Primary Examiner. 

1. A PROCESS FOR SELECTIVELY PLUGGINNG AN OIL-BEARING, SUBTERRANEAN, HIGH-PERMEABILITY AREA WHICH EXTENDS BETWEEN AND COMMUNICATES WITH FIRST AND SECOND WELL BORES SPACED APART FROM EACH OTHER, WHICH COMPRISES INTRODUCING CATALYZED RESIN-FORMING MATERIAL INTO SAID FIRST BORE AND THROUGH THE HIGH-PERMEABILITY AREA TO A POSITION AT LEAST ABOUT 60 PERCENT OF THE DISTANCE TO SAID SECOND BORE AT WHICH POSITION THE CATALYZED RESIN-FORMING AMTERIAL SETS TO PLUG SAID HIGH-PERMEABILITY AREA, AND PUMPING AT AN INCREASED PRESSURE FROM SAID FIRST BORE AN AMOUNT OF CATALYZED RESIN-FORMING MATERIAL INTO THE HIGH-PERMEABILITY AREA, SAID LATTER CATALYZED RESIN-FORMING MATERIAL BEING PUMPED AGAINST THE RESISTANCE OF PREVIOUSLY SET CATALYZED RESIN-FORMING MATERIAL, TO REGRESSIVELY PLUG THE HIGH-PERMEABILITY AREA FROM SAID POSITION TO A POSITION IN SAID AREA IN THE VICINITY OF SAID FIRST BORE, THEREBY PLUBBING AT LEAST ABOUT 60 PERCENT OF THE LENGTH OF THE HIGH-PERMEABILITY AREA. 